Fiber optic cable of significant length (e.g., 500-5000 meters) is presently being put into use for data and communication links among other things. As with electrical cable, it is often necessary to test and evaluate the cables for continuity and attenuation during manufacturing, as installed, or while in use. Continuity meters which measure line loss in decibels have been developed and put to use. Such meters function by passing light from a source of known intensity through the fiber optic cable under test and comparing the intensity of the light received to the known intensity of the light transmitted from the source to determine line losses due to attenuation. Attenuation losses are usually measured in relative quantities such as decibels.
A continuity or attenuation meter, like any other test instrument, must be calibrated. Heretofore, the calibration procedure has required that it be connected to a set of fiber optic cables of known length so that the continuity meter can be calibrated across its full range. This has meant retaining large lengths of standardized cable in the laboratory or taking the meter into the field for connection to cables of known length and attenuation. Such procedures are obviously inconvenient because they require either the storage of bulky cables or the inconvenience of having to transport the meter to be a remote site for calibration. In both instances, a number of standard length test cables must be connected and disconnected from the continuity meter. Thus, the test is not continuous across the full scale range of the meter.
Sometimes it is desirable to simulate the normal attenuation of a fiber optic cable of definite length for evaluation of an optical communication system. Therefore, there is a need for an instrument that will simulate fiber optic tables of definite length rather than use standard length test cables.
The present invention overcomes the aforesaid difficulties in calibrating a continuity or related type meter by providing a fiber optic cable attenuation simulator which accurately and repeatably simulates the attenuation in a fiber optic cable of extensive length.